The present invention relates generally to an exposure apparatus, an exposure method, and a device manufacturing method, and more particularly to an exposure apparatus, an exposure method, and a device manufacturing method that use an original, such as a reticle and a mask, which has a circuit or another pattern.
The pattern exposure technology that transfers an LSI pattern of a reticle onto a wafer is required to promote fine processing to a transferable pattern, and to reduce the cost of the exposure apparatus. In general, the exposure process uses a light blocking plate (field stop) called a masking blade to restrict a region of the light and to prevent the exposure light from reaching an unnecessary region on the reticle (mask). However, when a set exposure area of the masking blade is as large as an imaging pattern region, the device imaging precision lowers at and near a position corresponding to the aperture edge or contour in the masking blade due to the blur (or aberration) at the aperture edge. Therefore, a light shielding area is provided around the reticle pattern, and the masking blade is made wider in the opening direction by half the width of the light shielding area, preventing a degradation of the imaging precision. See, for example, Japanese Patent Application, Publication No. 2000-252193.
However, as the numerical aperture (“NA”) of the projection optical system becomes higher, the light can be reflected on the light shielding area, then on the reticle back surface that opposes to the patterned surface, and finally return to the reticle patterned surface. Then, the light is incident as the stray or unnecessary light upon the projection optical system and then the wafer at the adjacent part to the pattern transfer area, causing the critical dimension (“CD”) abnormality in the adjacent part. This phenomenon will be described with reference to FIG. 9. Here, FIG. 9 is a schematic view of the incident light upon the reticle when the aperture edge of the masking blade is set to the center of the light shielding area. 200 denotes the reticle, 201 the light shielding area, Ws a width of the light shielding area, and 202 the patterned area. The aperture edge of the masking blade is set to the center of the light shielding area 201 or at a position that shifts from the boundary between the patterned area 202 and the light shielding area 201 by Wi=Ws/2. Now address a ray OB1 corresponding to the aperture edge of the masking blade. The ray OB1 is incident upon the reticle at a comparatively small angel θc1, and reaches the reticle pattern plane. The ray OB1 is partially reflected onto the reticle back plane, and again partially reflected there onto the light shielding area 201. Thus, the ray OB1 is shielded by the light shielding area 201. On the other hand, a ray OB2 having an incident angle θc2 greater than the angle θc1 of the ray OB1 is reflected on the light shielding area 201 and then on the reticle back plane. The ray OB2 that returns to the reticle pattern plane leaks to the outside of the light shielding area 201. The ray OB2 passes the projection optical system, and reaches the adjacent area to the transfer area on the wafer, causing the CD abnormality that thickens or thins the CD there. A method of applying an antireflection film to the reticle back plane is one measure to avoid this phenomenon. See, for example, Japanese Patent Application, Publication No. 2005-031287.
However, the method of this reference forms the antireflection coating on the back plane of the reticle 20, and has a problem of making the reticle expensive. As a result, the manufacturing cost of the exposure apparatus using the reticle increases.
Another conceivable measure is to sufficiently widen the light shielding area, but the excessively wide light shielding part undesirably widens one exposure or shot area and lowers the device arrangement efficiency on the wafer.